The present invention relates generally to an image forming apparatus such as a copying machine, a printer, and a facsimile machine, and more particularly to a charging apparatus in which a roller type charging member is in pressure contact with an image bearing body.
A conventional electrophotographic image forming apparatus employs an image bearing body or a photoconductive drum. A spring urges a contact type charging roller against the photoconductive drum with a predetermined pressing force. The charging roller rotates in contact with the photoconductive drum, thereby uniformly charging the circumferential surface of the photoconductive drum.
However, the charging roller in pressure contact with the photoconductive drum suffers from a problem in that residual toner, external additive, and paper particles may adhere to the surface of the charging roller. Adhesion of foreign matter to the surface of the charging roller causes poor charging on a part of or over the entire circumferential surface of the photoconductive drum, resulting in poor print quality.
A solution to the problem has been proposed in which a cleaning member abuts the charging roller to clean the charging roller. Japanese Patent Publication No. 03-100676 discloses one such solution. A cleaning member or cleaning sponge is mounted to an inner wall of an image forming unit, being sandwiched under pressure between a charging roller and the inner wall.
The prior art disclosed in Japanese Patent Publication No. 03-100676 suffers from a problem in that the cleaning sponge and charging roller may not be assembled with high positional accuracy and therefore causes variations in the pressure exerted by the cleaning sponge on the charging roller.